Ventricular fibrillation threshold and vulnerable period in the isolated perfused rat heart.

Ventricular fibrillation threshold (VFT) measurements were obtained in the isolated perfused rat heart. Detailed morphology of the vulnerable period (VP) could be described by stimulating repeatedly at increasing levels of stimulus energy. Addition of lignocaine to the system caused an elevation of VGT, but also led to a delay of the VP to the end of the QT interval. The implications of these findings for the understanding of VFT measurements are discussed.